1. Field of the Invention
The invention relates to an electron-beam system for curing plastic layers on workpieces, having an irradiation chamber, an electron gun for generating at least one electron beam in the irradiation chamber, a transport device for conveying the workpieces into the irradiation chamber and out of the irradiation chamber, and a shield as radiation protection.
2. Description of the Prior Art
An electron-beam system disclosed in DE-A-20 04 050 includes vertically displaceable blocking devices provided directly upstream and downstream of the irradiation chamber and are used to shield against radiation emerging undesirably from the chamber openings in the irradiation chamber through which the workpieces are pushed into the irradiation chamber or guided out of it. In this device, the workpieces running horizontally through the irradiation chamber must be conveyed in the manner of "stop-and-go" traffic, that is to say it is necessary in each case to introduce one workpiece into the irradiation chamber, and it is then necessary to close the irradiation chamber at both ends. The transport device has to be briefly stopped in this process. After irradiation of the workpiece has been performed in the irradiation chamber, the two blocking devices are opened at the inlet end and the outlet end of the irradiation chamber, so that the finally irradiated workpiece can be removed from the irradiation chamber and a fresh workpiece can be transferred into the irradiation chamber. In order that, in this prior art, no scattered radiation (essentially, X-ray radiation generated by the high-energy electrons) can emerge from the irradiation chamber through the openings while the blocking device is being opened, it is necessary to provide complicated means so as to shield the electron beam during these times of opening the irradiation chamber.
In another known electron-beam system (DE 44 06 887 C1), provision is made of an irradiation chamber which, for the purpose of conveying plate-shaped workpieces in and away, cooperates with a transport device which forms a feed section and a discharge section, in addition to a shielding jacket above its transport section said transport device having in each case a conveying means with a plurality of shielding plates as a horizontal shield. In order to shield off the scattered radiation emerging in the region of a through opening from the irradiation chamber, the conveying means forming an orbit can be used for the purpose of continuously guiding said shielding plates into or out of their shielding position. In order to move these heavy shielding plates synchronously with the workpieces, the conveying means is provided with a technically complex design which is complicated to manipulate in the case of adaptation to changes in workpiece size. With the shielding jacket in the double-layered region of transport device and conveying means, the overall system is very large, and with the modules described above an inner cavity is formed below the shielding jacket and causes a disadvantageously high consumption of protective gas. Moreover, an expensive demounting of the shielding jackets causes difficulty in accessing the system in the region of the processing section, for example for the purposes of repair and maintenance.
A further known electron-beam system (DE-A-17 64 592) describes (FIG. 12) a conveying device for the workpieces to be irradiated, in the form of a rotary machine having separate chambers. The rotary machine is guided in a radiation-proof fashion in a spherical recess near the irradiation chamber, and the workpieces fall onto a belt conveyor after irradiation. This system is suitable only for relatively small workpieces which are suitable for being conveyed in a rotary machine.
It is the object of the invention to develop an electron-beam system of the type mentioned at the beginning in such a way that the system can achieve a high throughput of workpieces in conjunction with a low operating outlay, that the system can be adapted in a simple way to different workpiece dimensions, that reliable screening of the system against undesirable radiation is ensured, and that, in addition, it is also possible to save on the consumption of protective gas.